Frequency meter



Oct. 22, 19401 J. HATHAWAY 2 2 3 42 FREQUENCY METER Filed March 17, 1938 INVENTOR. JA RRE TT L. HATHA WAY A TTORNEY.

remade. 22, 1940- PATENT oFFicE 2.218.642 FREQUENCY METER Jarrett L. Hathaway, mama-N. in. assignor to Radio Corporation oi America, a corporation of Delaware Application March 11, 1938, Serial No. 198,393 14 Claims.- (01. 17%245) "I'hisinventlon relates to'direct reading electronic frequency meters and has for a primary object the measurement of frequencies from zero to several megacycles by electronic means.

Another object is to provide a simplified frequency meter which will have an accuracy comparable to other direct reading frequency meters.

I As far as I am aware, direct reading electronic frequency meters heretofore known and used have been inherently far more cumbersome than my improved device. Furthermore, they ordinarily have a restricted frequency range, the

usual maximum frequency measurable being in the neighborhood of 5,000 cycles per second. Due to limitations imposed by the elements used in previously known meters orcounters, it appears improbable that 'such circuits can be made to function satisfactorily much above 12,000 cycles per second.

Briefly, my inventioninvolves the application of the wave of unknown frequency to the grid circuit of a high gain thermionic discharge amplifier tube at sufllcient' amplitude to drive the grid of the tube far past cut- -oif on the negative grid swing, The output from this tube has a flat topped wave form with a wave front substantially independent of the shape of the input wave. Pulses derived from the output circuit are rectified and the resultant average direct current which varies in accordance with the input frequency is applied to a suitably calibrated meter.

A better understanding of the invention will be had by referring to the following detailed description which is accompanied by the drawing wherein Figure 1 illustrates an embodiment of my invention; Figures 1A, 1B and 1C illustrate modifications of the portion of Figure 1 to the right of the dotted line and Figure 2 shows another embodiment of my invention.

Referring, now, to Figure 1, reference nu-- circuitin order to prevent gridB from being driven appreciably positive. The input voltage must be sufiicient to drive .tube I sofar post cutoff that the slope of the wave from zero to negative cut-oil voltage is independent of the level in order to assure that the reading obtained is independent of the input amplitude. In order to prevent excessive input voltage requirements, a. high amplification tube is used with potentials on the elements adjustedso that grid cut-oif voltage is low. The-flat topped voltage pulses developed' across resistor 1 are applied to load'resistorl3 through condenser ll. These pulses are rectified by .rectifier tube 2 and the resultant rectified current pulses actuate meter It. With a fixed value of condenser II and of resistors l3 and I5 these pulses are of predetermined ampli- I. tude and wave shape, provided a suflicient, or more thansuiiicient, input level is used. .The number of these pulses per second increases with the input frequency thus creating a greater rectified average current through meter iii. If conll denser H or resistor l3 are decreased in value the width of the rectified current pulses decreases,

likewise decreasing the average current. Thus,

input. The voltage of this battery, should be about 1V2 volts. This may be variable, if desired,

in order to change the frequency range. 30

Figures 1A, 1B: and 10, which illustrate modifications .of the circuit of Figure l to the right of the dotted .line, show different meansof connecting the rectifier 2 and meter it. These changes may be desirable under certain circum- 85 stances. In Figure 1C acontact type rectifier 3 has been substituted for. the thermionic rectifier shown in the preceding figures." with this type of rectifier it maybe desirable to apply, by means of battery [4,- a bias voltage of proper-polarity 40 and amplitude, to overcomethe threshold re-- sistance of the contact rectifier.'-

The embodiment of my device shown in Figure '2 is quite similar to that shown in Figure l. In

order to make the device more compact tubes I 5 and 2 have beencombined in a single tube-I2 which contains a pentode amplifier and a diode rectifier. Transformeris used to isolate the grid from any direct current component in the, unknown frequency, as well as step up the-input 5 voltage. The operation of this circuit is the same as that of Figure 1. As shown in this figure no bias battery is required for the rectifier. du to the diode elements of the tube l2 being at the plus end of the filament and the return of of the proper range.

the meter circuit being connected to a more negative point in the circuit, that is, the minus end of the filament. Asshown in this figure a plurality of frequency ranges may be selected by selectively connecting into the circuit condensers ll, 2i and 22 by means oi switch 23. Meter I6 may be used to check filament or plate supply of voltages by means of switch 2t, as well as to indicate the "frequency. Multiplying resistances 25 and 2B are provided in the voltage checking circuits to convert the meter into a voltmeter Switch 27 is an oil-on switch. Obviously, Figure 2 may be modified in the same way as indicated for Figure 1 and Figures 1A, 1B and 1C.

While I have illustrated and described my particular arrangements for carrying the invention into effect my invention is by no means limited to the particular arrangements shown and described and modifications may be made without departing from the scope and spirit of the invention. 1

I claim:

1. In combination a thermionic discharge tube having a cathode, a grid and a plate, a pair of resistances connected in seriesbetween said grid and said cathode, an input circuit connected to said cathode and the junction between said pair of resistances, an output circuit for said tube including a resistance and a source of potential connected between said plate and said cathode, a condenser having one terminal connected to said plate, a fourth resistance connected between the other terminal of said condenser and said cathode, and a rectifier and a meter connected across said fourth resistance.

2. In combination a thermionic discharge tube having a cathode, a grid and a plate, a pair of resistances connected in series between said grid and said cathode, an input circuit connected to said cathode and the junction between said pair of resistances, an output circuit for said tube including a resistance and a source of potential connected between said plate and said cathode, a condenser having one terminal connected to said plate, a fourth resistance and a second source of potential connected between the other terminal of said condenser and said cathode and a rectifier and a meter connected across said fourth resistance and said second source of potential.

3. In combination a thermionic discharge tube having a cathode. a grid and a plate, an input circuit connectedv between said grid and cathode, an output-circuit for said tube including a resistance and a source ofpotential connected between said plate and said cathode, a condenser also connected to, said plate, a second resistance connected irom said condenser to said cathode and a rectifier and a meter connected in series across the second resistance. 5

4. In combination a thermionic discharge tube having a cathode, a grid and a plate, a resistance connected between said grid and cathode, means for applying an electric wave across said resistance, an output circuit for said tube including a resistance and a source 01' potential connected between said plate and said cathode, a condenser also connected to said plate, a third resistance connected from said condenser to said cathode and arectifier and a meter connected in series across the third'resistance, I

5. In combination a thermionic discharge tube having a cathode, a. grid and a plazta'an input circuit including a resistance connected between said grid and cathode, an output circuit for said tube including a. resistance and a source of potential connected between said plate and said cathode, a condenser also connected to said plate, a third resistance connected from said condenser to said cathode, a rectifier and a meter connected in series across said third resistance and a secand source of potential connected in series with said third resistance. 4

6. In combination a thermionic discharge tube having a cathode, a control grid, a screen grid and a plate, an input circuit including a resistance connected between said control grid and cathode, an output circuit for said tube including a resistance and a source of potential connected between said plate and said cathode, means connecting said screen grid to said source of potentie], a condenser also connected to said plate, a third resistance connected from said condenser to said cathode, a rectifier and a 'meter connected in series across said third resistance and a second source of potential connected in series with said third resistance.

7. In combination a thermionic discharge tube having a cathode, a grid and a plate, an input circuit including a resistance connected between said grid and cathode, an output circuit for said tube including a resistance and a source of potential connected between said plate and said cathode, a condenser also connected to said plate, a third resistance connected from said condenser to said cathode, a rectifier and a meter connected in series across said third resistor, a variable resistance in parallel with said meter and a second source of potential connected in series with said third resistance 8. In combination a thermionic discharge tube having a cathode, a control grid, a screen grid and a plate, an input circuit including a resistance connected between said control grid and cathode, an output circuit for said tube including a resistance and a source of potential connected between said plate and said cathode, means connecting said screen grid to said source ofpotential, a condenser also connected to said plate, a third resistance connected from said condenser to said cathode, a rectifier and a meter connected in series across said third resistor, a variable resistance in parallel with said meter and a second source of potential connected in series with said third resistance.

9. In combination a thermionic discharge tube having a cathodaa grid and a plate, an input circuit including a" resistance connected between said grid and cathode, an output circuit for said tube including a resistance and a source of potential connected between said plate and said cathode, a condenser also connected to said plate,

said grid and cathode, an output circuit for said tube including a resistance and a source of potential connected between said plate and said cathode, a condenser also connected to said plate, a third resistance connected from said condenser to said cathode, a rectifier and a variable resist ance connected in series across said third resistance and a meter shunting said variable resistor.

11. In combination a thermionic discharge tube hevinga filament, a pleteend control grid nected in series between said the end of said filament'remote from said second pole connected to said end, an input circuit conadapted to influence the electron flow betweeen said filament and said plate, a second plate at one end of said filament, a source of filament heating current having its positive pole connected to said end, an input circuit connected between said control grid and one end of said filament, a plate circuit connected between said first mentioned plate and the positive end of said filament and including a source of potential, a plurality of condensers connected to said plate, means for selectively connecting said condensers to said second plate and a resistance and a meter consecond plate and plate. v

12. In combination a thermionic discharge tube having a filament, a plate and control grid adapted to influence the electron flow between said filament and said plate, a second plate at one end of said filament, means for energizing said filament having its positive pole connected to said end, an input circuit connected between said control grid and theother end of said filament, a plate circuit connected between said first mentioned plate and the positive end of said filament and including a source of potential, a plurality of condensers connected to said plate,- means for selectively connecting said condensers to said second plate and a resistance and a meter connected in series between said second plate and the end of said filament remote from said second plate.

13. In combination a thermionic discharge tube having a'filament, a plate, a control grid adapted to influence the electron flow between said filament and plate and a screen grid, a second plate at one end of said filament, a source of filament'heating current having its positive filament heating current nected between said control grid and one end of said filament, a plate circuit connected between said first mentioned plate and the positive end of said filament and including a source of potential, means for connecting said screen grid to said source of potential, a plurality of condensers connected to said plate, means for selectively connecting said condensers to said second plate, a resistance and a meter connected in series between said second plate and the end of .said filament remote from said second plate.

14. In combination a thermionic discharge tube having a filament, a plate, a control grid adapted to influence the electron flow between said filament and plate and a screen grid, a sec- .ond plate at one end of said filament, a source of having its positive pole connected to said end, an input circuit connected between said control grid and one end of said filament, a plate circuit connected between said first mentioned plate and the positive-end of said filament and including a source of potential, means for connecting said screen grid to said source of potential, a plurality of condensers connected to said plate, means for selectively connecting said condensers to said second plate,

a resistance and a meter connected in series between said second plate and the end of said filament remote from said second plate, auxiliary resistances each having one end connected to the positive end of said source of filament heatingcurrent and said source of potential respectively, and means for selectively connecting said meter between the other end of said auxiliary resistances and the negative end of said sources.

J ARRE'I'I L. HATHAWAY. 

